The present invention relates to a vehicle seat assembly having a manual adjusting latch mechanism. The latch mechanism is provided with an irreversible pawl containing two sets of teeth to allow a tight engagement between the fixed and moving components of the latch mechanism while preventing reversal of tooth engagement under loading.
The use of a toothed pawl which engages a latch plate containing a plurality of locking apertures is a well known means of constructing a manually-operated latch to provide selective fore and aft movement of a seat in a vehicle. To facilitate engagement and to prevent backlash in the latch assembly, it is desirable to taper the edge surfaces of the pawl teeth to create a positive engagement angle so that the teeth may be wedge-fit into the openings in the latch plate upon release of the adjusting lever. In such a wedge fit, the angled surfaces of the teeth contact the edge of the locking apertures, resulting in a snug fit without backlash in the latch mechanism.
A tooth configuration employing wedged teeth therefore eliminates backlash in the latch mechanism. The engagement angle on each of the teeth must be made large enough to ensure an acceptable tooth length, since teeth which are too long are more prone to shear failure when loaded. However, a large engagement angle for the tooth surfaces facilitates disengagement of the teeth from the apertures under loading since the tapered teeth will then have a tendency to slide out of engagement along the wedging surfaces. A configuration employing only wedged teeth is therefore unacceptable because the engagement angle on each of the teeth must be so large to avoid an unacceptably long tooth that the resulting tooth configuration may be disengaged from the latch plate when subjected to loading, such as during a vehicle collision.
Consequently, it is an object of the present invention to provide a manual latch mechanism for a vehicle seat which possesses the desired characteristic of irreversibility under loading while eliminating backlash between the pawl teeth and locking apertures.
The teeth of the irreversible pawl of the present invention can be engaged and disengaged with the locking apertures in a latch plate by pulling on the seat adjusting lever. The present invention provides the pawl teeth with two sets of faces, inclined and parallel with respect to the locking apertures. In a particular embodiment of the invention, the pawl has two sets of teeth: one or both of the surfaces of the first set of teeth (the "wedging" teeth) are angled with respect to the locking apertures to form a positive engagement angle, providing a wedging fit. The surfaces of the second set of teeth (the "locking" teeth) are substantially parallel with the locking apertures to prevent movement and consequent disengagement when the seat is loaded.
Additionally, the width of the locking teeth may be chosen to provide a clearance fit between the teeth and the locking apertures, since the wedging surfaces on the wedging teeth already fit snugly in the locking apertures. Such a clearance fit facilitates easy engagement of the locking teeth with the locking apertures and allows for larger tolerances in the manufacture of the locking apertures.
Further objects, features, and advantages of the present invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.